My cleaner shrimp do that every 20-30 days. I know that they hatched cause they always seem to molt right after. I tryed to put some in the sump but the flow is too fast for them. I feed mysis and flakes (in the main tank) and I always see little shrimp stealing food and running around with pieces to big for them to eat. None have ever reached more then a centimeter or so, but they are without a doubt cleaner shrimp.